Parallels between playbacks and Pleistocene tar seeps suggest sociality in an extinct sabretooth cat, Smilodon. 2008. Biology Letters, published Tuesday, October 28, 2008.
From the press release:
Scientists from UCLA and the Zoological Society of London concluded that the sabertooth cat was social by comparing numbers of present-day carnivores competing for kills in Africa with those of mainly extinct species found in a North American fossil deposit.
Smilodon existed in North and South America between 1.8 million and 10,000 years ago and is one of the most common species preserved at the Rancho La Brea tar pits of Los Angeles, a fossil deposit in which dying herbivores trapped in sticky asphalt attracted numerous dire wolves and sabertooth cats, some of which also died there. Because most living cats are solitary, controversy has persisted over the social life of Smilodon.
The study took a new approach to the question by comparing data from the La Brea fossil record and data obtained from "playbacks" used in Africa, in which the recorded calls of distressed prey and the sounds of lions and hyenas are used to attract carnivores. This technique has been used by scientists to estimate carnivore densities in eastern and southern Africa.
Results showed that large social species made up a far larger proportion of the animals attracted than one would expect, considering their population size compared to other carnivores. Large social carnivores were, in fact, found to attend approximately 60 times more often than expected on the basis of relative abundance. When these results were compared with the records at the tar pits of California, the scientists found that the proportion of Smilodon records matched the proportion of the large social carnivores in the playbacks.
"The extinct sabertooth cat, Smilodon fatalis, has been something of an enigma, with almost nothing known of its behavior," said Chris Carbone, lead author of the paper. "This research allowed us to use the behavior of its present-day relatives to conclude that this extinct cat was more likely to roam in formidable gangs than as a secretive, solitary animal."
Friday, October 31, 2008
Thursday, October 30, 2008
Frenchman Formation Terrestrial Ecosystem Conference 2009
We are now accepting abstracts (up to six pages with illustrations) for posters and oral presentations, dealing with all aspects related to the late Maastrichtian palaeontology of the Frenchman Formation. The deadline for abstract submissions is March 1st, 2008. Registration will be $150 after March 1, but early registrants will receive a reduced rate of $100 for students and $125 for non-students. Your registration fee includes the abstract volume, banquet attendance, lunches, social events, and other benefits.
On May 20th there will be an optional workshop incorporating Frenchman Formation specimens, and fieldtrip to local macro- and microvertebrate sites. Cost for both fieldtrip (including lunch) and workshop is $40.
Please note that the conference will be limited to one hundred participants, so register soon. Conference information is available at dinocountry.com; click on T. rex Centre, and navigate to Coming Events. Registration fees can be paid by calling 306-295-4009 (FAX 306-295-4702), or by contacting t.rex1 @ sasktel.net. Proposed titles and abstracts should be sent to ffte2009 @ gmail.com.
T. rex Smells
Olfactory acuity in theropods: palaeobiological and evolutionary implications. 2008. D. Zelenitsky et al. Proc.Royal Soc. B Online.
The researchers inferred the size of the olfactory bulbs based on the impressions left on skull bones.
"T. rex has previously been accused of being a scavenger due to its keen sniffer, although its nose may point to alternative lifestyles based on what we see in living animals" says Zelenitsky, the lead investigator on the study. "Large olfactory bulbs are found in living birds and mammals that rely heavily on smell to find meat, in animals that are active at night, and in those animals that patrol large areas. Although the king of carnivorous dinosaurs wouldn't have passed on scavenging a free dead meal, it may have used its sense of smell to strike at night or to navigate through large territories to find its next victim."
In addition to providing clues about the biology and behavior of the ancient predators, the study also reveals some surprising information about the sense of smell in the ancestors of modern birds.
They found that the extinct bird Archaeopteryx, known to have evolved from small meat-eating dinosaurs, had an olfactory bulb size comparable to most theropod dinosaurs. Although sight is very good in most birds today, their sense of smell is usually poor, a pattern that does not hold true in the ancestry of living birds.
Scientists study dinosaur smelling skills for the first time and sniff out new angle on bird evolution.Scientists are providing new insight into the sense of smell of carnivorous dinosaurs and primitive birds, and have suggested that Tyrannosaurus rex had the best nose of all meat-eating dinosaurs. Their results tone down the reputation of T. rex as a scavenger [Ed. - Isn’t an enhanced sense of smell use to support the scavenging hypothesis?].
The researchers inferred the size of the olfactory bulbs based on the impressions left on skull bones.
"T. rex has previously been accused of being a scavenger due to its keen sniffer, although its nose may point to alternative lifestyles based on what we see in living animals" says Zelenitsky, the lead investigator on the study. "Large olfactory bulbs are found in living birds and mammals that rely heavily on smell to find meat, in animals that are active at night, and in those animals that patrol large areas. Although the king of carnivorous dinosaurs wouldn't have passed on scavenging a free dead meal, it may have used its sense of smell to strike at night or to navigate through large territories to find its next victim."
In addition to providing clues about the biology and behavior of the ancient predators, the study also reveals some surprising information about the sense of smell in the ancestors of modern birds.
They found that the extinct bird Archaeopteryx, known to have evolved from small meat-eating dinosaurs, had an olfactory bulb size comparable to most theropod dinosaurs. Although sight is very good in most birds today, their sense of smell is usually poor, a pattern that does not hold true in the ancestry of living birds.
Wednesday, October 29, 2008
Tuesday, October 28, 2008
Mitochondrial Phylogeny of the Extinct Cave Bear
Deciphering the complete mitochondrial genome and phylogeny of the extinct cave bear in the Paleolithic painted cave of Chauvet. 2008. C. Bon et al. PNAS Published online before print October 27, 2008.
Abstract: Retrieving a large amount of genetic information from extinct species was demonstrated feasible, but complete mitochondrial genome sequences have only been deciphered for the moa, a bird that became extinct a few hundred years ago, and for Pleistocene species, such as the woolly mammoth and the mastodon, both of which could be studied from animals embedded in permafrost.
To enlarge the diversity of mitochondrial genomes available for Pleistocene species, we turned to the cave bear (Ursus spelaeus), whose only remains consist of skeletal elements. We collected bone samples from the Paleolithic painted cave of Chauvet-Pont d'Arc (France), which displays the earliest known human drawings, and contains thousands of bear remains. We selected a cave bear sternebra, radiocarbon dated to 32,000 years before present, from which we generated overlapping DNA fragments assembling into a 16,810-base pair mitochondrial genome.
Together with the first mitochondrial genome for the brown bear western lineage, this study provides a statistically secured molecular phylogeny assessing the cave bear as a sister taxon to the brown bear and polar bear clade, with a divergence inferred to 1.6 million years ago.
With the first mitochondrial genome for a Pleistocene carnivore to be delivered, our study establishes the Chauvet-Pont d'Arc Cave as a new reservoir for Paleogenetic studies. These molecular data enable establishing the chronology of bear speciation, and provide a helpful resource to rescue for genetic analysis archeological samples initially diagnosed as devoid of amplifiable DNA.
and…
Isotopic evidence for omnivory among European cave bears: Late Pleistocene Ursus spelaeus from the Peştera cu Oase, Romania. 2008. M.P. Richards et al. PNAS 105 no. 2 600-604.
Abstract: Retrieving a large amount of genetic information from extinct species was demonstrated feasible, but complete mitochondrial genome sequences have only been deciphered for the moa, a bird that became extinct a few hundred years ago, and for Pleistocene species, such as the woolly mammoth and the mastodon, both of which could be studied from animals embedded in permafrost.
To enlarge the diversity of mitochondrial genomes available for Pleistocene species, we turned to the cave bear (Ursus spelaeus), whose only remains consist of skeletal elements. We collected bone samples from the Paleolithic painted cave of Chauvet-Pont d'Arc (France), which displays the earliest known human drawings, and contains thousands of bear remains. We selected a cave bear sternebra, radiocarbon dated to 32,000 years before present, from which we generated overlapping DNA fragments assembling into a 16,810-base pair mitochondrial genome.
Together with the first mitochondrial genome for the brown bear western lineage, this study provides a statistically secured molecular phylogeny assessing the cave bear as a sister taxon to the brown bear and polar bear clade, with a divergence inferred to 1.6 million years ago.
With the first mitochondrial genome for a Pleistocene carnivore to be delivered, our study establishes the Chauvet-Pont d'Arc Cave as a new reservoir for Paleogenetic studies. These molecular data enable establishing the chronology of bear speciation, and provide a helpful resource to rescue for genetic analysis archeological samples initially diagnosed as devoid of amplifiable DNA.
and…
Isotopic evidence for omnivory among European cave bears: Late Pleistocene Ursus spelaeus from the Peştera cu Oase, Romania. 2008. M.P. Richards et al. PNAS 105 no. 2 600-604.
Monday, October 27, 2008
It Was 20 Years Ago Today....
Last August some of the volunteers who came out to Dinosaur Provincial Park in 1988 as part of the Tyrrell Museum's volunteer program held a mini-reunion back in DPP. Unfortunately I could not attend (being en route to Mongolia), but my old friend Diane sent along some photos. Everyone still looks great!
Paul Ferguson, Maria Santi, Rita Schulze & Diane. Maria's wearing the field season t-shirt I designed for that year - a not-so-sly dig at the IMAX film crew that took up too much of our time that summer!
J.J. Henderson, Thompson Ferguson, Emily Henderson
The next Palaeo generation!: Thompson, J.J., Caroline Ferguson, & Emily
I could not find any 'before' pix from 1988, but I did find a series of photos showing the excavation in 1985 of the Daspletosaurus now on display at the RTMP Field Station in DPP. I'll post those soon.
Paul Ferguson, Maria Santi, Rita Schulze & Diane. Maria's wearing the field season t-shirt I designed for that year - a not-so-sly dig at the IMAX film crew that took up too much of our time that summer!
J.J. Henderson, Thompson Ferguson, Emily Henderson
The next Palaeo generation!: Thompson, J.J., Caroline Ferguson, & Emily
I could not find any 'before' pix from 1988, but I did find a series of photos showing the excavation in 1985 of the Daspletosaurus now on display at the RTMP Field Station in DPP. I'll post those soon.
Skull Shape & Crocodile Evolution
Cranial shape and correlated characters in crocodilian evolution. 2008. R. Sadleir and P. Makovivky. J. of Evol. Bio. 21: 1578 – 1596.
ABSTRACT: Crocodilians show a high degree of cranial variation and convergence throughout their 80 million-year fossil record that complicates their phylogenetic reconstruction. Conflicting phylogenetic results from different data partitions and character homoplasies typify crocodilian phylogeny, and differences between molecular and morphological phylogenetic hypotheses are believed to be associated with the slender-snout skull shape of Gavialis gangeticus and Tomistoma schlegelii. Slender-snout skulls are one of five identified eusuchian cranial ecomorph shape categories (ESCs) thought to reflect functional or ecological specialization.
This paper tested the effect of transitions among general, blunt and slender ESCs on cranial character-state distributions in phylogeny using the concentrated changes test. In addition, 'tree-free' character compatibility analysis of character independence was conducted on the morphological character matrix to determine if character correlations are observed independent of specific tree topologies.
Results suggest cranial ESCs do affect cranial character-state gains in phylogeny. Concentrated changes identify a broad suite of character-state changes that significantly correlate with transitions to slender, general and blunt ESCs on morphological, molecular and combined-data tree topologies, but numbers of correlated characters for each category differ according to topology.
Character compatibility analysis results do not mirror the concentrated changes test results and reflect hierarchically distributed support throughout the data. As cranial ESCs affect character-state transitions, it is possible that nonphylogenetic variables could affect inferences of crocodilian phylogeny by affecting cranial morphology.
This paper tested the effect of transitions among general, blunt and slender ESCs on cranial character-state distributions in phylogeny using the concentrated changes test. In addition, 'tree-free' character compatibility analysis of character independence was conducted on the morphological character matrix to determine if character correlations are observed independent of specific tree topologies.
Results suggest cranial ESCs do affect cranial character-state gains in phylogeny. Concentrated changes identify a broad suite of character-state changes that significantly correlate with transitions to slender, general and blunt ESCs on morphological, molecular and combined-data tree topologies, but numbers of correlated characters for each category differ according to topology.
Character compatibility analysis results do not mirror the concentrated changes test results and reflect hierarchically distributed support throughout the data. As cranial ESCs affect character-state transitions, it is possible that nonphylogenetic variables could affect inferences of crocodilian phylogeny by affecting cranial morphology.
Friday, October 24, 2008
Heterodontosaurus: Omnivore!
The teeth suggest Heterodontosaurus practiced occasional omnivory: the canines were used for defense or for adding small animals such as insects to a diet composed mainly of plants. Credit: Natural History Museum.
Heterodontosaurs, which means "different-toothed lizards," have an unusual combination of teeth, with large fang-like canines at the front of their jaws and worn, molar-like grinding teeth at the back. In contrast, most reptiles have teeth which change little in shape along the length of the jaw.
"It's likely that all dinosaurs evolved from carnivorous ancestors," said Laura Porro. "Since heterodontosaurs are among the earliest dinosaurs adapted to eating plants, they may represent a transition phase between meat-eating ancestors and more sophisticated, fully-herbivorous descendents."
Researchers suspect that the canines were used as defensive weapons against predators, or for adding occasional small animals such as insects, small mammals and reptiles to a diet composed mainly of plants--what the authors refers to as "occasional omnivory."
Heterodontosaurus also lacks replacement teeth, making it more similar to mammals, not only in the specialized, variable shape of its teeth but also in replacing its teeth slowly, if at all, and developing tight tooth-to-tooth contact. "Tooth replacement must have occurred during growth," the authors conclude, "however, evidence of continuous tooth replacement appears to be absent, in both adult and juvenile specimens."
Thanks to Sukie.
Development Stops The Evolution of Endless Forms
An End to Endless Forms: Epistasis, Phenotype Distribution Bias, and Nonuniform Evolution. 2008. E. Borenstein and D.C. Krakauer. PLoS Comput Biol 4(10): e1000202.
Diversity only a tiny fraction of the endless 'space' of possibilities, and observed phenotypes actually occupy only small, dense patches in the abstract phenotypic space. Researchers demonstrate that the sparseness of variety in nature can be attributed to the interactions between multiple genes and genetic controls involved in the development of organisms – a much simpler explanation than previously suggested.
The new model reproduces patterns that are observed in the fossil record, including increasing variation between taxonomic groups, accompanied by decreasing variation within groups. This pattern is consistent with the Cambrian radiation associated with a rapid proliferation of highly disparate, multicellular animals, and suggests that much of the variation seen today is as a result of simpler genetic controls dating from much earlier in evolutionary time.
The findings presented in this study also bear directly on issues of convergence (when very different organisms independently evolve similar features). By including a model of development, rather different genotypes can produce very similar phenotypes. Consequently, convergent evolution, which the vast space of genotypes would suggest to be rare, is allowed to become much more common.
One of the paradoxical implications of this study has been to show how innovations in development that lead to an overall increase in the number of accessible phenotypes, can lead to a reduction in selective variance. In other words, while the potential for novel phenotypes increases, the fraction of space these phenotypes occupies tends to contract. They concluded that "The theory presented in our paper complements the view of development as a key component in the production of endless forms and highlights the crucial role of development in constraining (as well as generating) biotic diversity."
Researchers have put forward a simple model of development and gene regulation that is capable of explaining patterns observed in the distribution of morphologies and body plans.From the press release:
Diversity only a tiny fraction of the endless 'space' of possibilities, and observed phenotypes actually occupy only small, dense patches in the abstract phenotypic space. Researchers demonstrate that the sparseness of variety in nature can be attributed to the interactions between multiple genes and genetic controls involved in the development of organisms – a much simpler explanation than previously suggested.
The new model reproduces patterns that are observed in the fossil record, including increasing variation between taxonomic groups, accompanied by decreasing variation within groups. This pattern is consistent with the Cambrian radiation associated with a rapid proliferation of highly disparate, multicellular animals, and suggests that much of the variation seen today is as a result of simpler genetic controls dating from much earlier in evolutionary time.
The findings presented in this study also bear directly on issues of convergence (when very different organisms independently evolve similar features). By including a model of development, rather different genotypes can produce very similar phenotypes. Consequently, convergent evolution, which the vast space of genotypes would suggest to be rare, is allowed to become much more common.
One of the paradoxical implications of this study has been to show how innovations in development that lead to an overall increase in the number of accessible phenotypes, can lead to a reduction in selective variance. In other words, while the potential for novel phenotypes increases, the fraction of space these phenotypes occupies tends to contract. They concluded that "The theory presented in our paper complements the view of development as a key component in the production of endless forms and highlights the crucial role of development in constraining (as well as generating) biotic diversity."
Thursday, October 23, 2008
Centrosaurus brinkmani Print by Mark Schultz Now Available
Art by Mark Schultz
Unlike some blogs I’ve never put up a “donation” link, and I have no plans to do this in the future. But, if you’d like to show your support for the blog & get a cool print, drop me a line.
All the money goes to support student research as part of the Southern Alberta Dinosaur Research Group’s on-going work, and, as such it’ll all be donated to the not-for profit Dinosaur Research Institute that administers these funds.
To see the complete print check out this previous posting.
Early Global Warming Produced New Form of Life
Gigantism in unique biogenic magnetite at the Paleocene–Eocene Thermal Maximum. 2008. Dirk Schumann et al. PNAS published ahead of print October 20, 2008.
From the press release:
Researchers have unearthed crystalline magnetic fossils of a previously unknown species of microorganism that lived at the boundary of the Paleocene and Eocene epochs, some 55 million years ago.
Though they are only some four microns long, these newly discovered, spear-shaped magnetite crystals (magnetofossils) – unearthed at a dig in New Jersey – are up to eight times larger than previously known magnetofossils. Magnetofossils are remnants of magnetite crystals produced by a type of bacteria called magnetotactic bacteria that are capable of orienting themselves along the direction of the Earth's magnetic field.
"Previous reports suggested that the source of the magnetic signature in the boundary layer was a type of magnetite that was formed by the impact of a comet," said lead researcher and corresponding author Dr. Hojatollah Vali. "In our previous paper we proved that the magnetic signature comes from biogenic material.
This species of microorganism, explained Vali, lived during a period of abrupt global warming known as the Paleocene-Eocene Thermal Maximum (PETM), when worldwide temperatures rose by 5° to 6° C over a period of 20,000 years.
From the press release:
Researchers have unearthed crystalline magnetic fossils of a previously unknown species of microorganism that lived at the boundary of the Paleocene and Eocene epochs, some 55 million years ago.
Though they are only some four microns long, these newly discovered, spear-shaped magnetite crystals (magnetofossils) – unearthed at a dig in New Jersey – are up to eight times larger than previously known magnetofossils. Magnetofossils are remnants of magnetite crystals produced by a type of bacteria called magnetotactic bacteria that are capable of orienting themselves along the direction of the Earth's magnetic field.
"Previous reports suggested that the source of the magnetic signature in the boundary layer was a type of magnetite that was formed by the impact of a comet," said lead researcher and corresponding author Dr. Hojatollah Vali. "In our previous paper we proved that the magnetic signature comes from biogenic material.
This species of microorganism, explained Vali, lived during a period of abrupt global warming known as the Paleocene-Eocene Thermal Maximum (PETM), when worldwide temperatures rose by 5° to 6° C over a period of 20,000 years.
Wednesday, October 22, 2008
Epidendrosaurus: Jurassic Feathered Dinosaur
A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. 2008. F. Zhang et al. Nature 455: 1105-1108.
Epidexipteryx, a new feathered dinosaur from the Jurassic Period, likely used its long tail feathers for display and possibly to help with balance while creeping along tree branches. Credit: Zhao Chuang & Xing Lida.
Abstract: Recent coelurosaurian discoveries have greatly enriched our knowledge of the transition from dinosaurs to birds, but all reported taxa close to this transition are from relatively well known coelurosaurian groups.
Here we report a new basal avialan, Epidexipteryx hui gen. et sp. nov., from the Middle to Late Jurassic of Inner Mongolia, China. This new species is characterized by an unexpected combination of characters seen in several different theropod groups, particularly the Oviraptorosauria. Phylogenetic analysis shows it to be the sister taxon to Epidendrosaurus, forming a new clade at the base of Avialae.
Epidexipteryx also possesses two pairs of elongate ribbon-like tail feathers, and its limbs lack contour feathers for flight. This finding shows that a member of the avialan lineage experimented with integumentary ornamentation as early as the Middle to Late Jurassic, and provides further evidence relating to this aspect of the transition from non-avian theropods to birds.
Epidexipteryx, a new feathered dinosaur from the Jurassic Period, likely used its long tail feathers for display and possibly to help with balance while creeping along tree branches. Credit: Zhao Chuang & Xing Lida.
Here we report a new basal avialan, Epidexipteryx hui gen. et sp. nov., from the Middle to Late Jurassic of Inner Mongolia, China. This new species is characterized by an unexpected combination of characters seen in several different theropod groups, particularly the Oviraptorosauria. Phylogenetic analysis shows it to be the sister taxon to Epidendrosaurus, forming a new clade at the base of Avialae.
Epidexipteryx also possesses two pairs of elongate ribbon-like tail feathers, and its limbs lack contour feathers for flight. This finding shows that a member of the avialan lineage experimented with integumentary ornamentation as early as the Middle to Late Jurassic, and provides further evidence relating to this aspect of the transition from non-avian theropods to birds.
Poached Eggs & Embryo Death in Modern Dinosaurs
Temperature-dependent sex-biased embryo mortality in a bird. 2008. Y. Eiby et al. Proceedings of the Royal Society B 275: 2703-2706.
Here, we investigated the causes of this temperature-dependent sex-biasing system. Molecular sexing of chicks and embryos confirmed that male embryo mortality was greater at high temperatures while female embryo mortality is greater at low temperatures, with mortality in both sexes similar at intermediate incubation temperatures. Temperature-dependent sex-biased embryo mortality represents a novel mechanism of altering sex ratios in birds. This novel mechanism, coupled with the unique breeding biology of the brush-turkey, offers a potentially unparalleled opportunity in which to investigate sex allocation theory in birds.
The idea that extreme temperature changes during the extinction event at the end of the Cretaceous played a role in the demise of the non-avian dinos has been mentioned a number of times over the past 20 years. Here’s some experimental evidence for the effect of temperature on the incubation of eggs from living birds.Abstract: Sex ratios have important evolutionary consequences and are often biased by environmental factors. The effect of developmental temperature on offspring sex ratios has been widely documented across a diverse range of taxa but has rarely been investigated in birds and mammals. However, recent field observations and artificial incubation experiments have demonstrated that the hatching sex ratio of a megapode, the Australian brush-turkey (Alectura lathami), varied with incubation temperature; more females hatched at high incubation temperatures and more males hatched at low temperatures.
Here, we investigated the causes of this temperature-dependent sex-biasing system. Molecular sexing of chicks and embryos confirmed that male embryo mortality was greater at high temperatures while female embryo mortality is greater at low temperatures, with mortality in both sexes similar at intermediate incubation temperatures. Temperature-dependent sex-biased embryo mortality represents a novel mechanism of altering sex ratios in birds. This novel mechanism, coupled with the unique breeding biology of the brush-turkey, offers a potentially unparalleled opportunity in which to investigate sex allocation theory in birds.
Overwintering Polar Dinos
Polar dinosaurs on parade: a review of dinosaur migration. 2008. P. Bell and E. Snively. Alcheringa 32: 271-284.
Certain groups also appear more predisposed to overwintering based on their physical inability (related to biomechanics, natural history, or absolute size) to migrate, such as ankylosaurs and many small taxa, including hypsilophodontids and troodontids. Low-nutrient subsistence is found to be the best overwintering method overall, although the likelihood that other taxa employed alternative means remains plausible. Despite wide distribution of some genera, species-level identification is required to assess the applicability of such distributions to migration distances. Presently, such resolution is not available or contradicts the migration hypothesis.
From the press release:
Bell does not dispute the evidence of migration and points to discoveries of large bone beds as evidence that many dinosaurs also traveled. In order to sustain the herd, "it seemed to make sense that they would be moving to and from the poles," he said.
While this view of migration is feasible for some species of polar dinosaurs, it does not hold for all, Bell noted. "Many types of dinosaurs were surviving in polar latitudes at the time, and getting along quite fine," said Bell. "They were not physically able to remove themselves from the environment for a variety of reasons and had to adapt to the cold, dark winters just as the rest of us mammals do today."
Contrary to popular belief, polar dinosaurs may not have traveled nearly as far as originally thought when making their bi-annual migration.Abstract: Cretaceous polar dinosaur faunas were taxonomically diverse, which suggests varied strategies for coping with the climatic stress of high latitudes. Some polar dinosaurs, particularly larger taxa such as the duckbill Edmontosaurus Lambe, 1917, were biomechanically and energetically capable of migrating over long distances, up to 2600 km. However, current evidence strongly suggests many polar dinosaurs (including sauropods, large and small theropods, and ankylosaurs of New Zealand) overwintered in preference to migration.
Certain groups also appear more predisposed to overwintering based on their physical inability (related to biomechanics, natural history, or absolute size) to migrate, such as ankylosaurs and many small taxa, including hypsilophodontids and troodontids. Low-nutrient subsistence is found to be the best overwintering method overall, although the likelihood that other taxa employed alternative means remains plausible. Despite wide distribution of some genera, species-level identification is required to assess the applicability of such distributions to migration distances. Presently, such resolution is not available or contradicts the migration hypothesis.
From the press release:
Bell does not dispute the evidence of migration and points to discoveries of large bone beds as evidence that many dinosaurs also traveled. In order to sustain the herd, "it seemed to make sense that they would be moving to and from the poles," he said.
While this view of migration is feasible for some species of polar dinosaurs, it does not hold for all, Bell noted. "Many types of dinosaurs were surviving in polar latitudes at the time, and getting along quite fine," said Bell. "They were not physically able to remove themselves from the environment for a variety of reasons and had to adapt to the cold, dark winters just as the rest of us mammals do today."
Monday, October 20, 2008
Dino Dance Floor
A Wet Interdune Dinosaur Trampled Surface in the Jurassic Navajo Sandstone, Coyote Buttes, Arizona: Rare Preservation of Multiple Track Types and Tail Traces. 2008. W. M. Seiler and M. A. Chan. Palaios 23: 700-710.
From the press release:
The three-quarter-acre site – which includes rare dinosaur tail-drag marks – provides more evidence there were wet intervals during the Early Jurassic Period, when the U.S. Southwest was covered with a field of sand dunes larger than the Sahara Desert.
Located within the Vermilion Cliffs National Monument, the site has more than 1,000 and perhaps thousands of dinosaur tracks, averaging a dozen per square yard in places. The tracks once were thought to be potholes formed by erosion. The site is so dense with dinosaur tracks that it reminds geologists of a popular arcade game in which participants dance on illuminated, moving footprints.
Seiler says the range of track shapes and sizes reveals at least four dinosaur species gathered at the watering hole, with the animals ranging from adults to youngsters.
The 6 cm-wide tail-drag marks – which are up to 7 m long – are a special discovery because there are fewer than a dozen dinosaur tail-drag sites worldwide, Seiler says. Four tail drags were within the 10 plots he surveyed, and there are others nearby.
"Dinosaurs usually weren't walking around with their tails dragging," he says.
University of Utah geologists identified an amazing concentration of dinosaur footprints that they call "a dinosaur dance floor," located in a wilderness on the Arizona-Utah border where there was a sandy desert oasis 190 million years ago.
The three-quarter-acre site – which includes rare dinosaur tail-drag marks – provides more evidence there were wet intervals during the Early Jurassic Period, when the U.S. Southwest was covered with a field of sand dunes larger than the Sahara Desert.
Located within the Vermilion Cliffs National Monument, the site has more than 1,000 and perhaps thousands of dinosaur tracks, averaging a dozen per square yard in places. The tracks once were thought to be potholes formed by erosion. The site is so dense with dinosaur tracks that it reminds geologists of a popular arcade game in which participants dance on illuminated, moving footprints.
Seiler says the range of track shapes and sizes reveals at least four dinosaur species gathered at the watering hole, with the animals ranging from adults to youngsters.
The 6 cm-wide tail-drag marks – which are up to 7 m long – are a special discovery because there are fewer than a dozen dinosaur tail-drag sites worldwide, Seiler says. Four tail drags were within the 10 plots he surveyed, and there are others nearby.
"Dinosaurs usually weren't walking around with their tails dragging," he says.
Sunday, October 19, 2008
Volcanic Origin For Life On Earth
The Miller Volcanic Spark Discharge Experiment. 2008. A. P. Johnson et al. Science 322: 404
Challengers of the Unknown © DC ComicsFrom the press release:
The original experiments, performed by Stanley Miller at the University of Chicago in 1953 and 1954 (Miller died in 2007), were the first to demonstrate that the basic molecules of life could be synthesized by subjecting hydrogen-rich gases (such as methane and ammonia) to an electric spark, simulating lightning in the primordial atmosphere. Scientists no longer think that the primordial atmosphere as a whole had the make-up assumed by Miller's experiments, but the clouds of gases emitted during volcanic eruptions do have a hydrogen-rich composition. Volcanic eruptions may have been very common during the planet's hot, early stages.
The apparatus used for Miller's original experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Image: Ned Shaw, Indiana University
"It turns out that some of the experiments Miller performed simulated the steam from volcanic eruptions, in addition to the more famous experiments that simulated a hydrogen-rich atmosphere," says H. James Cleaves, of the Carnegie Institution's Geophysical Laboratory, one of the paper's co-authors and Miller's last graduate student. "And when we analyzed samples left over from these volcanic experiments, they contained the most varied mixture of compounds."
Cleaves points out that lighting is very commonly associated with volcanic clouds, and could have been an abundant source of energy to convert simple compounds into organic molecules.
The apparatus used for Miller's "second," initially unpublished experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A tapering of the glass apparatus (inlay) creates a spigot effect, increasing air flow. A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Image: Ned Shaw, Indiana University
The building blocks of life may have emerged in volcanic eruptions on the early Earth, according to a new analysis of classic experiments performed more than fifty years ago. Using modern techniques to examine samples from the original experiments, researchers discovered previously undetectable organic compounds that point to the possible contribution of volcanism to the beginning of life on Earth.
Challengers of the Unknown © DC Comics
The original experiments, performed by Stanley Miller at the University of Chicago in 1953 and 1954 (Miller died in 2007), were the first to demonstrate that the basic molecules of life could be synthesized by subjecting hydrogen-rich gases (such as methane and ammonia) to an electric spark, simulating lightning in the primordial atmosphere. Scientists no longer think that the primordial atmosphere as a whole had the make-up assumed by Miller's experiments, but the clouds of gases emitted during volcanic eruptions do have a hydrogen-rich composition. Volcanic eruptions may have been very common during the planet's hot, early stages.
The apparatus used for Miller's original experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Image: Ned Shaw, Indiana University
Cleaves points out that lighting is very commonly associated with volcanic clouds, and could have been an abundant source of energy to convert simple compounds into organic molecules.
The apparatus used for Miller's "second," initially unpublished experiment. Boiled water (1) creates airflow, driving steam and gases through a spark (2). A tapering of the glass apparatus (inlay) creates a spigot effect, increasing air flow. A cooling condenser (3) turns some steam back into liquid water, which drips down into the trap (4), where chemical products also settle. Image: Ned Shaw, Indiana University
Crest Function In Hadrosaurs
Paleontologists have long debated the function of the strange, bony crests on the heads of the duck-billed dinosaurs known as lambeosaurs. The structures contain incredibly long, convoluted nasal passages that loop up over the tops of their skulls.From the press release:
Some paleontologists have suggested that the crests heightened the sense of smell by increasing the surface area of the sensory tissue. Others have argued that they regulated temperature, and still others have speculated that the crests acted as sound resonators for communication.
Scientists at the University of Toronto, Ohio University and Montana State University now have used CT-scanning to look inside these mysterious crests and reconstruct the brains and nasal cavities of four different lambeosaur species. At the annual meeting of the Society for Vertebrate Paleontology in Cleveland, Ohio, the team today announced new findings that suggest the crests were used for communication.
"Even though the soft tissues are not preserved in the fossils, the shape of the bones that encase the brain and nasal passages are," said David Evans. "From there, the anatomy of these missing soft parts is easily interpreted."
The portion of the brain responsible for the sense of smell was relatively small and primitive, indicating that the crest did not evolve to improve that sense.
Computer models done by other researchers suggest that the crests could have been used to make low, eerie bellowing calls that could have been used in communication, perhaps to call for mates or warn others of predators.
The CT scans documented a delicate inner ear that confirms that the dinosaurs could hear the low-frequency calls produced by the crest.
"We were surprised to see just how large the centers of the brain associated with higher cognitive functions were," said Witmer. "We suspected that the crested duck-billed dinosaurs used both vocal and visual displays, but now we see that they had the brain power and hearing to pull off these behaviors."
Wednesday, October 15, 2008
The Skull of Tiktaalik
The cranial endoskeleton of Tiktaalik roseae. 2008. J. Downs et al. Nature 455: 925-929.
Today, the team that discovered Tiktaalik in the Canadian Arctic provided new details of its transition from water to solid ground. Further examination of the fossils shows a coordinated series of changes underway not just in the creature's limbs, but in its crocodile-like skull, neck and gills, all helping prepare it for a less aquatic, shallow-water lifestyle.
The researchers published their results today in the journal Nature and discussed them publicly during a symposium at this morning's meeting of the Society of Vertebrate Paleontology meeting in Cleveland.
Read the full story by John Mangels in the Cleveland Plain Dealer.
Today, the team that discovered Tiktaalik in the Canadian Arctic provided new details of its transition from water to solid ground. Further examination of the fossils shows a coordinated series of changes underway not just in the creature's limbs, but in its crocodile-like skull, neck and gills, all helping prepare it for a less aquatic, shallow-water lifestyle.
The researchers published their results today in the journal Nature and discussed them publicly during a symposium at this morning's meeting of the Society of Vertebrate Paleontology meeting in Cleveland.
Read the full story by John Mangels in the Cleveland Plain Dealer.
The SVP conference is progressing very well. I'll post some photos, etc., when I get a chance.
Today In History: Darwin Accepted Into Cambridge
From Today In Science History:
In 1827, Charles Darwin was accepted
into Christ's College at Cambridge, but did not start until winter term because he needed to catch up on some of his studies. He had entered the University of Edinburgh in 1825 to study medicine, intending to follow his father Robert's career as a doctor. However, Darwin found himself unenthusiastic about his studies, including that of geology.
Disappointing his family that he gave up on a medical career, he left Edinburgh without graduating in April 1827. His scholastic achievements at Cambridge were unremarkable, but after graduation, Darwin was recommended by his botany professor to be a naturalist to sail on HM Sloop Beagle
In 1827, Charles Darwin was accepted
into Christ's College at Cambridge, but did not start until winter term because he needed to catch up on some of his studies. He had entered the University of Edinburgh in 1825 to study medicine, intending to follow his father Robert's career as a doctor. However, Darwin found himself unenthusiastic about his studies, including that of geology. Disappointing his family that he gave up on a medical career, he left Edinburgh without graduating in April 1827. His scholastic achievements at Cambridge were unremarkable, but after graduation, Darwin was recommended by his botany professor to be a naturalist to sail on HM Sloop Beagle
Monday, October 13, 2008
Dinos & The Cretaceous Terrestrial Revolution
Dinosaurs and the Cretaceous Terrestrial Revolution. 2008. G.T. Lloyd et al. Proceedings of the Royal Society B 275: 2483-2490.
Click to enlarge
Abstract: The observed diversity of dinosaurs reached its highest peak during the mid- and Late Cretaceous, the 50Myr that preceded their extinction, and yet this explosion of dinosaur diversity may be explained largely by sampling bias. It has long been debated whether dinosaurs were part of the Cretaceous Terrestrial Revolution (KTR), from 125–80Myr ago, when flowering plants, herbivorous and social insects, squamates, birds and mammals all underwent a rapid expansion.
Although an apparent explosion of dinosaur diversity occurred in the mid-Cretaceous, coinciding with the emergence of new groups (e.g. neoceratopsians, ankylosaurid ankylosaurs, hadrosaurids and pachycephalosaurs), results from the first quantitative study of diversification applied to a new supertree of dinosaurs show that this apparent burst in dinosaurian diversity in the last 18 Myr of the Cretaceous is a sampling artefact. Indeed, major diversification shifts occurred largely in the first one-third of the group's history.
Despite the appearance of new clades of medium to large herbivores and carnivores later in dinosaur history, these new originations do not correspond to significant diversification shifts. Instead, the overall geometry of the Cretaceous part of the dinosaur tree does not depart from the null hypothesis of an equal rates model of lineage branching. Furthermore, we conclude that dinosaurs did not experience a progressive decline at the end of the Cretaceous, nor was their evolution driven directly by the KTR.
Click to enlarge
Although an apparent explosion of dinosaur diversity occurred in the mid-Cretaceous, coinciding with the emergence of new groups (e.g. neoceratopsians, ankylosaurid ankylosaurs, hadrosaurids and pachycephalosaurs), results from the first quantitative study of diversification applied to a new supertree of dinosaurs show that this apparent burst in dinosaurian diversity in the last 18 Myr of the Cretaceous is a sampling artefact. Indeed, major diversification shifts occurred largely in the first one-third of the group's history.
Despite the appearance of new clades of medium to large herbivores and carnivores later in dinosaur history, these new originations do not correspond to significant diversification shifts. Instead, the overall geometry of the Cretaceous part of the dinosaur tree does not depart from the null hypothesis of an equal rates model of lineage branching. Furthermore, we conclude that dinosaurs did not experience a progressive decline at the end of the Cretaceous, nor was their evolution driven directly by the KTR.
Subscribe to:
Posts (Atom)